China has drawn “red lines” in key ecological areas with fragile environments in 15 provincial regions to strengthen protection, the Ministry of Environmental Protection announced on Monday.

Approved by the State Council, or the country’s cabinet, the protection zones defined by the red lines cover a total of 610,000 square kilometers, or about 25 percent of the land area in these regions, according to the ministry.

The ministry and the National Development and Reform Commission, the country’s top economic planner, will guide and help the other provincial regions draw red lines by the end of this year.

Red line, or hongxian, is frequently used in China to describe a limit that should not be crossed.

Last February, the central authorities issued a document that makes determining red lines for ecological protection a national strategy.

The document stresses that the principle of ecological protection red lines is to strictly regulate and manage areas where development is prohibited according to the law, on the basis of safeguarding the nation’s ecology and maintaining its ecological functions.

By the end of 2020, China should have clearly defined the red lines, according to the document.